Insulating layer-forming compositions, also called intumescent compositions, are generally applied to the surface of components for the purpose of forming coatings, in order to protect the components from fires or against extreme heat exposure due, for example, to a fire. Steel structures are now an inherent part of modern architecture, even if they have a distinct disadvantage as compared to reinforced concrete steel construction. Above approximately 500° C., the load-bearing capacity of steel drops by 50%, i.e., the steel loses its stability and its load-bearing capacity. This temperature may already be reached after approximately 5 to 10 minutes, depending on the fire load, for example, in the case of direct exposure to fire (approximately 1,000° C.), which frequently results in a loss of load-bearing capacity of the structure. The goal of fire protection, in particular of steel fire protection in the event of fire, is to prolong as long as possible the time span up to the loss of the load-bearing capacity of a steel structure, in order to save human lives and valuable assets.
For this purpose, the building codes of many countries require corresponding fire resistance times for particular buildings made of steel. They are defined by so-called F-classes, such as F 30, F 60, F 90 (fire resistance classes according to DIN 4102-2) or American classes according to ASTM, etc. F 30, for example, according to DIN 4102-2 means that in the event of fire, a supporting steel structure under standard conditions must be able to withstand the fire for at least 30 minutes. This is normally achieved in that the heating rate of the steel is slowed, for example, by covering the steel structure with insulating layer-forming coatings. This involves painted coats, the components of which expand in the event of fire, while forming a solid microporous carbon foam. Formed in the process is a fine-pored and thick foam layer, the so-called ash crust, which, depending on the composition, is highly heat insulating and thus slows the heating of the component, so that the critical temperature of approximately 500° C. is reached at the earliest after 30, 60, 90, 120 minutes or up to 240 minutes. Essential for the achievable fire resistance is invariably the layer thickness of the coating applied or the ash crust produced by it. Closed profiles, such as pipes, given comparable solidity, require approximately double the amount as compared to open profiles, such as supports having a double-T profile. In order to adhere to the required fire resistance times, the coatings must have a certain thickness and, when exposed to heat, must be capable of forming an advantageously voluminous and therefore well-insulating ash crust, which remains mechanically stable for the duration of the fire load.
There exist various systems in the prior art for such purpose. Essentially, a distinction is drawn between 100% systems and solvent-based or water-based systems. In solvent-based systems or water-based systems, binding agents, usually resins, are applied as a solution, dispersion or emulsion to the components. These may be implemented as single component systems or multi-component systems. The solvent or water, once it is applied, evaporates and leaves behind a film which dries over time. A further distinction may be drawn in this case between systems, in which the coating essentially no longer changes during drying, and systems in which, after evaporation, the binding agent cures primarily as the result of oxidation reactions and polymerization reactions, which are induced, for example, by the oxygen from the atmosphere. The 100% systems contain the components of the binding agent without a solvent or water. They are applied to the component, the “drying” of the coating taking place merely by reacting the binding agent components with one another.
The solvent-based systems or water-based systems have the disadvantage that the drying times, also called curing times, are long and, moreover, multiple layers must be applied, i.e., require multiple work steps, in order to achieve the required layer thickness. Since each individual layer must be correspondingly dried prior to application of the next layer, the result is more hours of labor and correspondingly high costs on the one hand, and a delay in the completion of the building structure, since in part several days pass, depending on the climatic conditions, before the required layer thickness is applied. Also disadvantageous is the fact that because of the required layer thickness, the coating may tend to form cracks and to peel during drying or when exposed to heat, as a result of which, in the worst case, the subsurface is partially exposed, in particular in systems in which the binding agent does not re-harden after the solvent or the water evaporates.
In order to overcome this disadvantage, epoxy-amine-based two-component systems or multi-component systems have been developed, which involve almost no solvents, so that a curing occurs significantly more rapidly and, in addition, thicker layers may be applied in one work step, so that the required layer thickness is built up significantly more rapidly. However, these systems have the disadvantage that the binding agent forms a very stable and rigid polymer matrix, often with a high softening range, which inhibits the formation of foam by the foaming agent. For this reason, thick layers must be applied in order to produce a sufficient foam thickness for the insulation. This, in turn, is disadvantageous, since it requires a large amount of material. To be able to apply these systems, processing temperatures of up to +70° C. are frequently required, which makes the application of such systems labor-intensive and their installation costly. Moreover, some of the binding agent components used are toxic or otherwise problematic (for example, irritating, caustic), such as, for example, the amines or amine mixtures used in the epoxy-amine systems.